downstream: net/dcb: check for detached device before executing callbacks

When a netdevice is detached there is no point in trying to execute
the dcb callbacks; at best they will return stale information, and
at worst crash the machine.

Fixes: 2f90b86 ("ixgbe: this patch adds support for DCB to the kernel and ixgbe driver")
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Denis Kirjanov <kirjanov@gmail.com>
Signed-off-by: Haonan Fang <fanghaonan@bytedance.com>

Author: kda88

net/dcb/dcbnl.c

@@ -1943,7 +1943,7 @@ static int dcb_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
 		return -EINVAL;
 
 	netdev = __dev_get_by_name(net, nla_data(tb[DCB_ATTR_IFNAME]));
-	if (!netdev)
+	if (!netdev || !netif_device_present(netdev))
 		return -ENODEV;
 
 	if (!netdev->dcbnl_ops)